This invention relates to a power train for a power shift transmission mainly having a rearward driving speed stage and plural forward driving speed stages.
In a work vehicle, for example, such as a truck crane equipped with the above power train, a large tractive force or travelling at ultra-low speed may sometimes be required. However, it has been difficult in a conventional power train to provide, for example, only a forward driving first stage with a large speed reduction ratio in preparation for the above-mentioned case requiring a large tractive force. First of all, a conventional embodiment will be described hereunder according to FIG. 1 which shows a power train having four forward driving stages and one rearward driving stage. In FIG. 1, 1 is a forward driving first speed clutch, and 2 is a forward driving second speed clutch. The forward driving first speed clutch 1 engages a first input shaft 3 for the forward driving first speed with and disengages it from a first output shaft 4 therefor, and the forward driving second speed clutch 2 engages a second input shaft 5 for the forward driving second speed with and disengages it from a second output shaft 6 therefor. The second output shaft 6 is interconnected through a gear 7, a gear 8 (a third output shaft 9) and a gear 10 to a driven shaft 11, and the driven shaft 11 is interconnected, for example, through a differential mechanism to a wheel axle etc. The second input shaft 5 is always interconnected through gears 14, 15 to the first input shaft 3. However, a driving shaft 17 interconnected to an engine 16 is always interconnected through gears 18, 19 to the first input shaft 3, so that a reduction gear set effective only for the forward driving first speed is merely one set consisting of reduction gears 20, 21 installed between the first output shaft 4 and the second output shaft 6. Accordingly, an attempt to make only the reduction ratio of the forward first speed large has been difficult by using only the set of the gears 20, 21 due to limitation of mumber of teeth, etc. 23 is a forward driving third speed clutch, 24 is a forward driving fourth speed clutch, 25 is a rearward driving clutch, and 26 is an idle gear. FIG. 2 is a diagram showing a relation between a travelling speed V and a tractive force P in a conventional embodiment, wherein A.sub.1, A.sub.2, A.sub.3, and A.sub.4 show the forward driving first speed, the forward driving second speed, the forward driving third speed, and the forward driving fourth speed respectively. Namely, it will be understood that not only the reduction ratio of the first forward driving speed is especially made large. Incidentally, FIG. 1a is a drawing showing relative positions of each shaft viewing in the direction of the arrow I.sub.a of FIG. 1.
An object of this invention is to make it possible to enlarge a reduction ratio effective only for a forward driving first speed without constructing a power train to a large size.
In order to accomplish the above object, in this invention, a first input shaft and a first output shaft on the same axis engaged and disengaged through a forward driving first speed clutch and a second input shaft and a second output shaft on the same axis engaged and disengaged through a forward driving second speed clutch are disposed in parallel with a driving shaft on an engine side, the driving shaft is interconnected through transmission gears to the second input shaft and at the same time the second output shaft is interconnected to the driven shaft side such as an axle etc., both the input shafts are interconnected through a forward driving first speed first reduction gear set, and both the output shafts are interconnected through the forward driving first speed second reduction gear set.